Variable power optical system

ABSTRACT

Liquid lens cells are used in a variable power optical system. In one embodiment, a stop is located between a first lens group comprising at least a first liquid lens cell and a second lens group comprising at least a second liquid lens cell. In one embodiment, a liquid lens cell controls an incident angle of light rays on an image surface.

RELATED APPLICATIONS

This application is a divisional of U.S. application Ser. No.12/753,536, filed Apr. 2, 2010, which claims priority benefit of U.S.Provisional 61/168,524 filed Apr. 10, 2009. The entirety of each of theforegoing applications are hereby incorporated by reference herein andmade a part of the present specification.

BACKGROUND

The present invention relates to a variable power optical systememploying liquid optics.

A zoom lens will often have three or more moving lens groups to achievethe zoom and focusing functions. A mechanical cam may link two movablelens groups to perform zooming, and a third movable lens group may beused for focus.

The zoom range is determined in part by the range of movement for themovable lens elements. Greater zoom ranges may require additional spacefor movement of the lens elements.

Image sensors, such as charge coupled device (CCD) sensors and CMOSimage sensors (CIS) collect light using a small photosensitive area suchas a photodiode. The image sensors may use micro-lenses to improvephotosensitivity by collecting and focusing light from a large lightcollecting area. The incident angle of light reaching the micro-lens orphotosensitive area affects the amount of light collected by thephotosensitive area, with light that is received at some angles beingless likely to reach the photosensitive area than light that is receivedat other angles.

Ideally, the incident angle of light at the photosensitive area isconstant. However, as a zoom lens varies the focal length, the incidentangle of light may change. Thus, moving a lens through the range of zoompositions may result in undesirable results as the incident anglechanges.

SUMMARY

A variably power optical component may be used to minimize variations inthe incident angle of light on an image surface.

In one embodiment, a variable power optical system comprises a firstlens group with at least a first liquid lens cell, a second lens groupwith at least a second liquid lens cell, and a third liquid lens cellconfigured to control an incident angle of light rays on a sensor. Thecontrol of a zoom position is substantially based at least in part onthe configuration of the optical power of the first liquid lens cell andthe configuration of the optical power of the second liquid lens cell.The stop may be approximately equidistant between a first surface of thefirst lens group and a last surface of the second lens group. A diameterof the first liquid lens cell is about the same as a diameter of thesecond liquid lens cell. In one embodiment, the zoom range is greaterthan about 3×. In one embodiment, the zoom range is greater than about4×. In one embodiment, the zoom range is greater than about 5×.

In one embodiment, an optical system is arranged to collect radiationemanating from an object space and deliver radiation to an image surfacein an image space along a common optical axis. A first variable poweroptical component that is stationary on the common optical axiscomprises at least two liquids with different refractive properties andat least one contact surface between the two liquids. The shape of thecontact surface is varied to produce a change of optical power in thevariable power optical component, resulting in a variation of a chiefray angle approaching an image point on the image surface. A secondvariable power optical component comprises at least two liquids withdifferent refractive properties and at least one contact surface betweenthe two liquids. The shape of the contact surface is varied to reducethe variation in the chief ray angle at the image point on the imagesurface caused by varying the shape of the first variable power opticalcomponent. The shape of the first variable power optical component maybe varied to provide a zoom and/or a focus function.

In one embodiment, a variable power objective optical system uses noaxially moving groups. At least one variable power optical componentprovides a zoom function comprising at least two liquids with differentrefractive properties and at least one contact surface between the twoliquids. The shape of the contact surface is varied to produce a changeof optical power in the variable power optical component. Anothervariable power optical component comprises at least two liquids withdifferent refractive properties and at least one contact surface betweenthe two liquids. The shape of the contact surface is varied to at leastpartially compensate for changes in variation of a chief ray angleapproaching an image point on the image surface caused by variable poweroptical component that provides a zoom function.

In one embodiment, a variable power optical system comprises a firstlens group with at least a first liquid lens cell, a second lens groupwith at least a second liquid lens cell, and a stop located between thefirst lens group and the second lens group. Light rays passing throughthe first lens group, second lens group, and the stop represent a zoomposition, with control of the zoom position based at least in part onthe configuration of the optical power of the first liquid lens cell andthe configuration of the optical power of the second liquid lens cell.The stop may be approximately equidistant between a first surface of thefirst lens group and a last surface of the second lens group. The zoomrange may be greater than 3× in one embodiment. The zoom range may begreater than 4× in one embodiment. The zoom range may be greater than 5×in one embodiment.

In one embodiment, a variable power objective optical system comprisesat least one variable power optical component with at least two liquidswith different refractive properties and at least one contact surfacebetween the two liquids. The shape of the contact surface is varied toat least partially compensate for changes in variation of a chief rayangle approaching an image point on an image surface. The variation ofthe chief ray angle may be caused at least in part by, for example, azoom function, a focus function, or a combination of a zoom function anda focus function.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A and 1B are optical diagrams depicting rim rays for an axiallight beam in a variable power optical system employing liquids.

FIGS. 2A and 2B are optical diagrams depicting rim rays for an axiallight beam and rims rays for an off-axis field beam in a variable poweroptical system employing liquids.

FIGS. 3A, 3B, 3C, 3D and 3E illustrate various incident angles of lightrays on an image surface.

FIGS. 4A and 4B illustrate use of a liquid lens cell to adjust anincident angle of a light ray on an image surface.

FIGS. 5A, 5B, 5C, 5D and 5E illustrate optical diagrams of an exemplaryvariable power optical system design.

FIG. 6 is a block diagram of a camera.

DETAILED DESCRIPTION

In the following description, reference is made to the accompanyingdrawings. It is to be understood that other structures and/orembodiments may be utilized without departing from the scope of theinvention.

Liquid lens cells can modify an optical path without relying uponmechanical movement of the liquid cell. A liquid lens cell comprisingfirst and second contacting liquids may be configured so that acontacting optical surface between the contacting liquids has a variableshape that may be substantially symmetrical relative to an optical axisof the liquid lens cell. A plurality of lens elements could be alignedalong a common optical axis and arranged to collect radiation emanatingfrom an object side space and delivered to an image side space. Theliquid lens cell could be inserted into an optical path formed by theplurality of lens elements that are aligned along the common opticalaxis. The optical axis of the liquid lens cell could be parallel to thecommon optical axis, or it could be at an angle or decentered to thecommon optical axis.

Presently contemplated liquid lens systems will have a difference inrefractive index of about 0.2 or more, preferably at least about 0.3,and in some embodiments at least about 0.4. Water has a refractive indexof about 1.3, and adding salt may allow varying the refractive index toabout 1.48. Suitable optical oils may have a refractive index of atleast about 1.5. Even by utilizing liquids with higher, lower or higherand lower refractive indices, for example a higher refractive index oil,the range of power variation remains limited. This limited range ofpower variation usually provides less magnification change than that ofa movable lens group. Therefore, in a simple variable power opticalsystem, to provide zooming while maintaining a constant image surfaceposition most of the magnification change may be provided by one movablelens group and most of the compensation of defocus at the image surfaceduring the magnification change may be provided by one liquid cell.

It should be noted that more movable lens groups or more liquid cells,or both, may be utilized. Examples of one or more moving lens groupsused in combination with one or more liquid cells is described in U.S.patent application Ser. No. 12/246,224 titled “Liquid Optics Zoom Lensand Imaging Apparatus,” filed Oct. 6, 2008, and incorporated byreference in its entirety.

The size and properties of lens elements used in a system introduceconstraints to be considered in designing the lens system. For example,the diameter of one or more lens elements may limit the size of an imageformed on an image surface. For lens systems with variable properties,such as a variable power optical system, the optics may change based onvariation of the lens elements. Thus, a first lens element may constraina lens system in a first zoom configuration, while a second lens elementconstrains the lens system in a second zoom configuration. As anexample, the rim rays for a light beam may approach the outer edge of alens element at one extreme of the zoom range, while being a significantdistance from the outer edge of the same lens element at the otherextreme of the zoom range.

FIGS. 1A and 1B illustrate optical diagrams of a simplified variablepower optical system that employs liquid lens cells. The variable poweroptical system may be used, for example, with a camera. In FIG. 1A, afirst liquid lens cell LLC1 20 and a second liquid lens cell LLC2 22 areconfigured so that the zoom ratio is in the wide position. An imaginglens 24 forms the image on an image surface (which is illustrated as animage plane 26) corresponding with a camera pick-up device. The imaginglens 24 may be a liquid lens cell or other lens type. The rim rays 12 ofan axial light beam illustrated in FIG. 1A are near the outer edge ofliquid lens cell LLC2 22. Accordingly, the diameter of liquid lens cellLLC2 22 is a limiting factor in the lens design. In FIG. 1B, liquid lenscell LLC1 20 and liquid lens cell LLC2 22 are configured so that thezoom ratio is in the telephoto position. The rim rays 12 of the axiallight beam illustrated in FIG. 1B are near the outer edge of liquid lenscell LLC1 20, making the diameter of liquid lens cell LLC1 the limitingfactor. Thus, the simplified design illustrated in FIGS. 1A and 1B isoptimized to fully take advantage of the area on liquid lens cell LLC120 and liquid lens cell LLC2 22 for the rim rays 12 of axial light beamsbetween a range of positions.

Traditional zoom lens systems utilize moving zoom lens groups to achievedifferent zoom positions. Because the variable power optical systemillustrated in FIGS. 1A and 1B utilizes liquid lens cells, moving lensgroups are not needed. Instead, a control system may be used to controlthe variable shape of the contacting optical surface in liquid lenscells LLC1 20 and LLC2 22.

The use of liquid lens cells instead of moving lens groups facilitatesplacement of the stop 10 between liquid lens cells LLC1 20 and LLC2 22.Because the liquid lens cells LLC1 20 and LLC2 22 are not moving lensgroups, there is no concern that stop 10 will interfere with theirproper operation. Stop 10 does not need to be equidistant between theliquid lens cells, and placement of the stop can be optimized as needed.

It is to be understood that liquid lens cells LLC1 20 and LLC2 22 couldeach comprise multiple surfaces, with the surfaces being controllableand/or fixed. In some embodiments, the liquid lens cells illustrated inFIGS. 1A and 1B could comprise a combination of two or more liquidcells. A plate may be placed between the combined cells. The plate mayhave an optical power that may be set as desired for the design. Theliquid lens cells may also have plates on the exterior surfaces. In someembodiments, the plates on the exterior surfaces may provide opticalpower or a folding function. The plates and other lens elements can bespherical or aspherical to provide improved optical characteristics.

The individual lens elements may be constructed from solid-phasematerials, such as glass, plastic, crystalline, or semiconductormaterials, or they may be constructed using liquid or gaseous materialssuch as water or oil. The space between lens elements could contain oneor more gases. For example normal air, nitrogen or helium could be used.Alternatively the space between the lens elements could be a vacuum.When “Air” is used in this disclosure, it is to be understood that it isused in a broad sense and may include one or more gases, or a vacuum.The lens elements may have coatings such as an ultraviolet ray filter.

FIGS. 2A and 2B illustrate additional optical diagrams of the simplifiedvariable power optical system of FIGS. 1A and 1B, depicting rim rays 12for an axial light beam and rim rays 14 for an off-axis field beam. Thechief ray 16 of the off-axis field beam crosses the optical axis at thestop location 10, the stop location indicated by tick marks external tothe rim rays. As illustrated, the incident angle 18 of the chief ray 16of the off-axis field beams on the image plane 26 changes as the zoomlens changes from the wide position to the telephoto position.

The angle of incidence is important because it determines, to someextent, the amount of light that reaches an image sensor. An imagesensor may use micro-lenses to improve photosensitivity by collectingand focusing light from a large light collecting area. However, if thesize and range of incident angles through zoom are too large, themicro-lenses may not be able to direct the light to the image sensor forefficient sensing through zoom.

Consider FIGS. 3A-3D, which provide exemplary illustrations of lightreaching an image sensor. In FIG. 3A, the incident angle 18 of the chieflight ray 28 is perpendicular to the image sensor, allowing a micro-lensto successfully direct the light rays to the image sensor. FIGS. 3B and3C also have small variances of incident angles 18. The micro-lens arraycould be shifted to form an optimized micro array of lenses, allowingsuccessful redirection of the light rays to the image sensor. FIGS. 3Dand 3E have larger variances in, and size of, the incident angles 18,making it more difficult for a micro-lens to direct the rays to theimage sensor.

Because the incident angle 18 of the chief light ray 28 changes as thevariable power optical system changes from the wide position to thetelephoto position, it is possible that the incident angle 18 for onezoom position could be as illustrated in FIG. 3B, while the incidentangle 18 for another zoom position could be as illustrated in FIG. 3C.However, it may be desirable to reduce the variations of the incidentangle 18.

FIGS. 4A and 4B illustrate optical diagrams where a liquid lens cellLLC3 30 is placed near the image sensor. As the variable power opticalsystem moves through the zoom range, the optical power of the liquidlens cell LLC3 also varies. The variable optical power of the liquidlens cell LLC3 30 allows minimization of the variance in, and size of,the incident angle on the image surface throughout the zoom range. Forexample, in one embodiment, the liquid lens cell LLC3 provides for theincident angle to be less than 10° from perpendicular to the image plane26. In another embodiment, the liquid lens cell LLC3 provides for theincident angle to be less than 5° from perpendicular.

Although FIGS. 4A and 4B illustrate lens 30 as a liquid lens cell, othertypes of lenses may also be used. Lengthening the overall variable poweroptical design may allow a standard lens to be used instead of a liquidlens cell.

The length of the variable power optical system depends, in part, on therange of optical powers provided by the liquid lens cells. The length ofthe lens can be minimized by utilizing liquid lens cells that have ahigh index difference of the liquids. The length of the lens may also beminimized by utilizing multiple liquid lens cells and/or folding.

For simplification, FIGS. 1A, 1B, 2A, 2B, 4A and 4B show lens elementsas plates which contain optical power. It is to be understood that thelens elements could be comprised of multiple components with differentlens materials and/or optical surfaces.

FIGS. 5A-5E illustrate optical diagrams of an exemplary variable poweroptical design. FIG. 5A illustrates the wide position, and FIG. 5Eillustrates the telephoto position. FIGS. 5B-5D illustrate theintermediate zoom positions. Infinity focus is used for all the zoompositions illustrated in FIGS. 5A-5E.

This variable power optical design utilizes five liquid lens cells 40,42, 44, 46 and 48, with each liquid lens cell having a variable surface50, 52, 54, 56, and 58. The lens group near the object space includestwo liquid lens cells 40, 42 and is used to primarily assist inproviding focus and zoom. The variable power optical design alsoincludes two liquid cells 44, 46 that are used to primarily assist inproviding zoom. In the illustrated embodiment, the stop 60 is betweenthe lens group comprising liquid lens cells 40, 42 and the lens groupcomprising liquid lens cells 44, 46. The variable power optical designalso includes a liquid lens cell 48 which partly provides for control ofthe incident angle at the image plane 62. In combination all five liquidlenses together provide control of focus, zoom and the incident angle ofthe chief ray of the off-axis field beams on the image plane as thevariable power optical system changes from the wide position to thetelephoto position and from infinity focus to close focus.

As illustrated in FIGS. 5A-5D, the optical power provided by variablesurface 54 remains fairly constant, and only changes significantly inFIG. 5E. This illustrates that if the zoom positions are limited to therange shown in FIGS. 5A-5D, liquid lens cell 44 could be replaced with afixed lens element. Accordingly, the number of liquid lens cells couldvary with the design requirements.

For the lens design shown in FIGS. 5A-5E, a listing produced by theCodeV optical design software version 9.70 commercially available fromOptical Research Associates, Pasadena, Calif. USA is attached hereto aspart of this specification and incorporated by reference in itsentirety.

FIG. 6 illustrates a block diagram of a camera 100 with a variable poweroptical system 102. FIG. 6 also illustrates a lens control module 104that controls the movement and operation of the lens groups in opticalsystem 102. The control module 104 includes electronic circuitry thatcontrols the radius of curvature in the liquid lens cells. Theappropriate electronic signal levels for various focus positions andzoom positions can be determined in advance and placed in one or morelookup tables. Alternatively, analog circuitry or a combination ofcircuitry and one or more lookup tables can generate the appropriatesignal levels. In one embodiment, a polynomial is used to determine theappropriate electronic signal levels. Points along the polynomial couldbe stored in one or more lookup tables or the polynomial could beimplemented with circuitry. The lookup tables, polynomials, and/or othercircuitry may use variables for zoom position, focus position,temperature, or other conditions.

Thermal effects may also be considered in the control of the radius ofcurvature of surface between the liquids. The polynomial or lookup tablemay include an additional variable related to the thermal effects.

The control module 104 may include preset controls for specific zoomsettings or focal lengths. These settings may be stored by the user orcamera manufacturer.

FIG. 6 further illustrates an image capture module 106 that receives anoptical image corresponding to an external object. The image istransmitted along an optical axis through the optical system 102 to theimage capture module 106. The image capture module 106 may use a varietyof formats, such as film (e.g., film stock or still picture film), orelectronic image detection technology (e.g., a CCD array, CMOS device orvideo pickup circuit). The optical axis may be linear, or it may includefolds.

Image storage module 108 maintains the captured image in, for example,on-board memory or on film, tape or disk. In one embodiment, the storagemedium is removable (e.g., flash memory, film canister, tape cartridgeor disk).

Image transfer module 110 provides transferring of the captured image toother devices. For example, the image transfer module 110 may use one ora variety of connections such as, for example, a USB port, IEEE 1394multimedia connection, Ethernet port, Bluetooth wireless connection,IEEE 802.11 wireless connection, video component connection, or S-Videoconnection.

The camera 100 may be implemented in a variety of ways, such as a videocamera, a cell phone camera, a digital photographic camera, or a filmcamera.

The liquid cells in the focus and zoom groups could be used to providestabilization, as described in U.S. patent application Ser. No.12/327,666 titled “Liquid Optics Image Stabilization,” filed Dec. 3,2008, and incorporated by reference in its entirety. By using non-movinglens groups, folds may be used to reduce the overall size as describedin U.S. patent application Ser. No. 12/327,651 titled “Liquid Opticswith Folds Lens and Imaging Apparatus,” filed Dec. 3, 2008, andincorporated by reference in its entirety. One or more moving lensgroups may be used in combination with one or more liquid cells asdescribed in U.S. patent application Ser. No. 12/246,224 titled “LiquidOptics Zoom Lens and Imaging Apparatus,” filed Oct. 6, 2008, andincorporated by reference in its entirety.

It is to be noted that various changes and modifications will becomeapparent to those skilled in the art. Such changes and modifications areto be understood as being included within the scope of the invention asdefined by the appended claims.

1. A variable power optical system, comprising: a first lens group,wherein the first lens group comprises at least a first liquid lenscell; a second lens group, wherein the second lens group comprises atleast a second liquid lens cell; and a stop located between the firstlens group and the second lens group, wherein light rays passing throughthe first lens group, second lens group, and the stop represent a zoomposition, with control of the zoom position based at least in part onthe configuration of the optical power of the first liquid lens cell andthe configuration of the optical power of the second liquid lens cell.2. The variable power optical system of claim 1, wherein the stop isapproximately equidistant between a first surface of the first lensgroup and a last surface of the second lens group.
 3. The variable poweroptical system of claim 1, wherein a diameter of the first liquid lenscell is about the same as a diameter of the second liquid lens cell. 4.The variable power optical system of claim 1, wherein the zoom range isgreater than about 3×.
 5. The variable power optical system of claim 1,wherein the zoom range is greater than about 4×.
 6. The variable poweroptical system of claim 1, wherein the zoom range is greater than about5×.
 7. A variable power optical system, comprising: a first lens group,wherein the first lens group comprises at least a first liquid lenscell; a second lens group, wherein the second lens group comprises atleast a second liquid lens cell; and a third liquid lens cell configuredto control an incident angle of light rays on a sensor, wherein controlof a zoom position is based at least in part on the configuration of theoptical power of the first liquid lens cell and the configuration of theoptical power of the second liquid lens cell.
 8. The variable poweroptical system of claim 7, wherein control of the zoom position is basedat least in part on the configuration of the optical power of the thirdliquid lens cell.
 9. The variable power optical system of claim 7,further comprising a stop located between the first lens group and thesecond lens group.